The present invention provides initiators for nitroxide-mediated radical polymerization (NMP) processes.
In conventional radical polymerization processes, the polymerization terminates when reactive intermediates are destroyed or rendered inactive; radical generation is essentially irreversible. It is often difficult to control the molecular weight and the polydispersity (molecular weight distribution) of polymers produced by conventional radical polymerization, in order to achieve a highly uniform and well-defined product. It is also often difficult to control radical polymerization processes with the degree of certainty necessary in specialized applications, such as in the preparation of end functional polymers, block copolymers, star (co)polymers, and other novel topologies.
In a controlled radical polymerization process radicals are generated reversibly, and irreversible chain transfer and chain termination are absent. There are four major controlled radical polymerization methodologies: atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), nitroxide-mediated polymerization (NMP) and iniferters, each method having advantages and disadvantages.
Nitroxide mediated radical polymerization (NMP) has been described as a simple, versatile and efficient controlled radical polymerization process. See, e.g., C. J. Hawker et al., xe2x80x9cNew Polymer Synthesis by Nitroxide Mediated Living Radical Polymerizationsxe2x80x9d, Chemical Reviews, 2001, pp. 3661-3688. NMP processes employ an alkoxy amine as an initiator to produce a polymeric radical in the presence of a monomer.
There is a need for a radical polymerization process which provides telechelic (co)polymers having a predictable molecular weight and a narrow molecular weight distribution (low xe2x80x9cpolydispersityxe2x80x9d). A further need is for a radical polymerization process which is sufficiently flexible to provide a wide variety of products, but which can be controlled to the degree necessary to provide highly uniform products with a controlled structure (i.e., controllable topology, composition, etc.). There is further need for a controlled radical polymerization process which provides telechelic (co)polymers capable of entering into further polymerization or functionalization through reactive end-groups, particularly electrophilic end groups.
In one aspect, the present invention provides initiators for nitroxide-mediated radical polymerization processes that comprise compounds of the Formula I: 
wherein X is H, an alkyl group, a cycloalkyl group, a heterocyclic group, an arenyl group, an aryl group, a cyano group, an acyl group or the residue of a free-radical initiator;
R1 is H, an alkyl group, a cycloalkyl group, a heterocyclic group, an arenyl group or an aryl group;
ON(R2)2 is the residue of an organonitroxide;
R3 and R4 are independently selected from an alkyl, a cycloalkyl group, an aryl group, an arenyl group, or R3 and R4 taken together with the carbon to which they are attached form a carbocyclic ring;
Q is a linking group selected from a covalent bond, (xe2x80x94CH2xe2x80x94)oxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94(CH2)oxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94(CH2CH2O)oxe2x80x94, xe2x80x94COxe2x80x94NR6xe2x80x94(CH2)oxe2x80x94,xe2x80x94COxe2x80x94Sxe2x80x94(CH2)oxe2x80x94, where o is 1 to 12, and R6 is H, an alkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group or an aryl group;
each n is 0 or 1;
q is 0 or 1; and
m is 0 to 20.
The present invention also provides initiators that comprise the ring-opened reaction product of the initiators of Formula I and a reactive compound, such as an aliphatic compound, having one or more nucleophilic groups. Such initiators have the general Formula II: 
wherein
X is an H, an alkyl group, a cycloalkyl group, a heterocyclic group, an arenyl group, an aryl group, a nitrile, an acyl group or the residue of a free-radical initiator,
R1 is H, an alkyl group, a cycloalkyl group, a heterocyclic group, an arenyl group or an aryl group;
ON(R2)2 is the residue of an organonitroxide;
R3 and R4 are each independently selected from an alkyl, a cycloalkyl group, an aryl group, an arenyl group, or R3 and R4 taken together with the carbon to which they are attached form a carbocyclic ring;
Q is a linking group selected from a covalent bond, (xe2x80x94CH2xe2x80x94)o, xe2x80x94COxe2x80x94Oxe2x80x94(CH2)oxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94(CH2CH2O)oxe2x80x94, xe2x80x94COxe2x80x94NR6xe2x80x94(CH2)oxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94(CH2)oxe2x80x94, where o is 1 to 12, and R6 alkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group or an aryl group;
each n is 0 or 1;
q is 0 or 1;
m is 0 to 20;
Z is 0, S or NR6, wherein R6 is H, an alkyl group, a cycloalkyl group, an arenyl group, a heterocyclic group or an aryl group;
R5 is an organic or inorganic moiety and has a valency of p, R5 is the residue of a mono- or polyfunctional compound of the formula R5(ZH)p.
The initiators of the present invention provide (co)polymers having a predictable molecular weight and a narrow molecular weight distribution. Advantageously, the initiators provide novel multireactive addition polymers having first and second terminal reactive groups that may be used for further functionalization. The present invention further provides a controlled radical polymerization process useful in the preparation of terminal-functionalized (telechelic) (co)polymers, block copolymers, star (co)polymers, graft copolymers, and comb copolymers. The process provides these (co)polymers with controlled topologies and compositions.
The control over molecular weight and functionality obtained in this invention allows one to synthesize numerous materials with many novel topologies for applications in coatings, surface modifications, elastomers, sealants, lubricants, pigments, personal care compositions, composites, inks, adhesives, water treatment materials, hydrogels, imaging materials, telechelic materials and the like.
In another aspect, the invention provides a method for polymerization of one or more olefinically unsaturated monomers comprising addition polymerizing one or more olefinically unsaturated monomers using the azlactone initiators of Formula I, or the ring-opened azlactone initiators of Formula II.
It is to be understood that the recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).
It is to be understood that all numbers and fractions thereof are presumed to be modified by the term xe2x80x9cabout.xe2x80x9d
It is to be understood that xe2x80x9caxe2x80x9d as used herein includes both the singular and plural.
The general definitions used herein have the following meanings within the scope of the present invention.
The term xe2x80x9calkylxe2x80x99 refers to straight or branched, cyclic or acyclic hydrocarbon radicals, such as methyl, ethyl, propyl, butyl, octyl, isopropyl, tert-butyl, sec-pentyl, cyclohexyl, and the like. Alkyl groups include, for example, 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms, or most preferably 1 to 6 carbon atoms.
The term xe2x80x9carylxe2x80x9d means the monovalent residue remaining after removal of one hydrogen atom from an aromatic compound which can consist of one ring or two fused rings having 6 to 12 carbon atoms.
The term xe2x80x9carenylxe2x80x9d means the monovalent residue remaining after removal of a hydrogen atom from the alkyl portion of a hydrocarbon containing both alkyl and aryl groups having 6 to 26 atoms.
The term xe2x80x9cazlactonexe2x80x9d means 2-oxazolin-5-one groups and 2-oxazolin-6-one groups of Formula I, where n is 0 and 1, respectively.
The term xe2x80x9cheterocyclic groupxe2x80x9d or xe2x80x9cheterocyclexe2x80x9d means the monovalent residue remaining after removal of one hydrogen atom from an cycloaliphatic or aromatic compound having one ring or two fused rings having 5 to 12 ring atoms and 1 to 3 heteroatoms selected from S, N, and nonperoxidic O. Useful heterocycles include azlactonyl, pyrrolyl, furan, thiophenyl, imidazolyl, pyrazolyl, thiazolyl, oxazolyl, pyridinyl, piperazinyl, piperidinyl, hydrogenated and partially hydrogenated derivatives thereof
The term xe2x80x9cmultifunctionalxe2x80x9d means the presence of more than one of the same functional reactive group;
The term xe2x80x9cmultireactivexe2x80x9d means the presence of two or more of two different functional reactive groups;
The term xe2x80x9cpolyfunctionalxe2x80x9d is inclusive of multireactive and multifunctional.
The term xe2x80x9cmolecular weightxe2x80x9d means number average molecular weight (Mn), unless otherwise specified.
The term (co)polymer refers to homo- and copolymers.
The term (meth)acrylate refers to both methacrylate and acrylate.